Photoresist patterning process supporting two step phosphor-deposition to form an led matrix array

ABSTRACT

A method is described for low temperature curing of silicone structures, including the steps of providing patterning photoresist structures on a substrate. The photoresist structures define at least one open region that can be at least partially filled with a condensation cure silicone system. Vapor phase catalyst deposition is used to accelerate the cure of the condensation cure silicone, and the photoresist structure is removed to leave free standing or layered silicone structures. Phosphor containing silicone structures that are coatable with a reflective metal or other material are enabled by the method.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/715,930 filed on Dec. 16, 2019, which claims priority to EuropeanPatent Application 19156331.1 filed Feb. 11, 2019 and to U.S.Provisional Patent Application 62/783,970 filed Dec. 21, 2018, each ofwhich is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure generally relates to a patterning process thatallows curing of silicones or siloxanes without substantially harmingpatterned photoresist release properties. Manufacture of reflectivewalled phosphor pixel arrays for an LED matrix array is one embodimentenabled using the disclosed patterning process.

BACKGROUND

Low temperature patterning of silicone using conventional positivephotoresists can be difficult. The temperatures required to curesilicone are typically higher than temperatures needed to ensure cleanremoval of photoresist, preventing general usage of photoresistpatterned silicone. Processes that allow for low temperature curing ofsilicone in conjunction with photoresist patterning structures areneeded.

This limitation can prevent use of photoresist patterning forsemiconductor light-emitting devices (LEDs). LED arrays can bemanufactured to include pixels formed from a combination of an LED arraywith an overlaying array of phosphors embedded in silicone. However,since temperatures required to cure phosphor containing silicone aretypically higher than temperatures needed to ensure clean removal ofphotoresist, improved processes that work for patterning silicones usingphotoresist structures are needed.

As another example, to improve LED efficiency and operation, light fromLED arrays can be arranged to pass from a top of each member of the LEDarray, through respectively matched phosphor/silicone array, with somepercentage being wavelength converted to provide a needed light spectraloutput. Typically, some proportion of the light is lost by reflection ordirect transmission out the side of the phosphor layer. To minimize thisloss and crosstalk with neighboring pixels, reflective materials can beused to coat sidewalls of each pixel of the phosphor/silicone array.However, when LEDs are closely positioned next to each other in anarray, it is difficult to uniformly coat the sidewalls. Improvedprocesses and structures that allow for forming such reflective coatedphosphor/silicone structures using are needed.

SUMMARY

In accordance with embodiments of the invention, a method is describedfor low temperature curing of silicone structures, including the stepsof providing patterned photoresist structures on a substrate. Thephotoresist structures define at least one open region that can be atleast partially filled with a condensation cure silicone system. Vaporphase catalyzation is used to cure the condensation cure siliconesystem, the photoresist structure is removed to leave free standing orlayered silicone structures.

In some embodiments the condensation cure silicone system furtherincludes organosiloxane block copolymers.

In some embodiments vapor phase catalyzation further includes use ofsuperbase catalyzing agents, which can include but are not limited touse of 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU).

In another embodiment, a method for defining phosphor containingsilicone structures suitable for receiving light from LED elements isdisclosed. The method includes the steps of providing patterningphotoresist structures on a substrate, with the photoresist structuresdefining at least one open region. The at least one open region is atleast partially filled with a phosphor particle containing condensationcure silicone system. The condensation cure silicone system can then becured after vapor-phase catalyst deposition or concurrently with vaporphase catalyst deposition. The photoresist structure is removed, andsilicon bound phosphor particles coated with a reflective material.Cavities defined by the structures of bound phosphor particles can befilled with additional bound phosphor particles, leaving vertical wallsof reflective material.

In some embodiments, checkerboard structures can be defined by boundphosphor particles coated with a reflective material. Reflectivematerial can be removed from a top or a bottom of the checkboardstructures to leave vertically arranged walls of reflective materialpositioned only between the checkerboard structures.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the present disclosureare described with reference to the following figures, wherein likereference numerals refer to like parts throughout the various figuresunless otherwise specified.

FIG. 1 shows a schematic cross-sectional view of an example pcLED.

FIGS. 2A and 2B show, respectively, cross-sectional and top schematicviews of an array of pcLEDs.

FIG. 3A shows a schematic top view an electronics board on which anarray of pcLEDs may be mounted, and FIG. 3B similarly shows an array ofpcLEDs mounted on the electronic board of FIG. 3A.

FIG. 4A shows a schematic cross sectional view of an array of pcLEDsarranged with respect to waveguides and a projection lens. FIG. 4B showsan arrangement similar to that of FIG. 4A, without the waveguides.

FIG. 5 is a flow chart illustrating an example process for patterningsilicones using photoresist structures.

FIGS. 6A, 6B, 6C, 6D, 6E, 6F, and 6G illustrate steps in an examplemethod of manufacturing silicone and phosphor structures for LEDpackages.

FIG. 7 illustrates an intermediate checkerboard structure prior toinfill with silicone and phosphor material.

DETAILED DESCRIPTION

The following detailed description should be read with reference to thedrawings, in which identical reference numbers refer to like elementsthroughout the different figures. The drawings, which are notnecessarily to scale, depict selective embodiments and are not intendedto limit the scope of the invention. The detailed descriptionillustrates by way of example, not by way of limitation, the principlesof the invention.

FIG. 1 shows an example of an individual pcLED 100 comprising asemiconductor diode structure 102 disposed on a substrate 104, togetherconsidered herein an “LED”, and a phosphor layer 106 disposed on theLED. Semiconductor diode structure 102 typically comprises an activeregion disposed between n-type and p-type layers. Application of asuitable forward bias across the diode structure results in emission oflight from the active region. The wavelength of the emitted light isdetermined by the composition and structure of the active region.

The LED may be, for example, a III-Nitride LED that emits blue, violet,or ultraviolet light. LEDs formed from any other suitable materialsystem and that emit any other suitable wavelength of light may also beused. Other suitable material systems may include, for example,III-Phosphide materials, III-Arsenide materials, and II-VI materials.

Any suitable phosphor materials may be used, depending on the desiredoptical output from the pcLED.

FIGS. 2A-2B show, respectively, cross-sectional and top views of anarray 200 of pcLEDs 100 including phosphor pixels 106 disposed on asubstrate 202. Such an array may include any suitable number of pcLEDsarranged in any suitable manner. In the illustrated example the array isdepicted as formed monolithically on a shared substrate, butalternatively an array of pcLEDs may be formed from separate individualpcLEDs. Substrate 202 may optionally comprise CMOS circuitry for drivingthe LED, and may be formed from any suitable materials.

As shown in FIGS. 3A-3B, a pcLED array 200 may be mounted on anelectronics board 300 comprising a power and control module 302, asensor module 304, and an LED attach region 306. Power and controlmodule 302 may receive power and control signals from external sourcesand signals from sensor module 304, based on which power and controlmodule 302 controls operation of the LEDs. Sensor module 304 may receivesignals from any suitable sensors, for example from temperature or lightsensors. Alternatively, pcLED array 200 may be mounted on a separateboard (not shown) from the power and control module and the sensormodule.

Individual pcLEDs may optionally incorporate or be arranged incombination with a lens or other optical element located adjacent to ordisposed on the phosphor layer. Such an optical element, not shown inthe figures, may be referred to as a “primary optical element”. Inaddition, as shown in FIGS. 4A-4B a pcLED array 200 (for example,mounted on an electronics board 300) may be arranged in combination withsecondary optical elements such as waveguides, lenses, or both for usein an intended application. In FIG. 4A, light emitted by pcLEDs 100 iscollected by waveguides 402 and directed to projection lens 404.Projection lens 404 may be a Fresnel lens, for example. This arrangementmay be suitable for use, for example, in automobile headlights. In FIG.4B, light emitted by pcLEDs 100 is collected directly by projection lens404 without use of intervening waveguides. This arrangement mayparticularly be suitable when pcLEDs can be spaced sufficiently close toeach other, and may also be used in automobile headlights as well as incamera flash applications. A microLED display application may usesimilar optical arrangements to those depicted in FIGS. 4A-4B, forexample. Generally, any suitable arrangement of optical elements may beused in combination with the pcLEDs described herein, depending on thedesired application.

For many uses of pcLED arrays, it is desirable to compartmentalize thelight emitted from the individual pcLEDs in the array. That is, it isadvantageous to be able to operate an individual pcLED in the array as alight source while adjacent pcLEDs in the array remain dark. This allowsfor better control of displays or of illumination.

It is also advantageous in many applications to place the pcLEDs in thearray close together. For example, a preferred configuration inmicroLEDs is to have minimal spacing between the individual LEDs.Closely spacing the pcLEDs in an array used as a camera flash lightsource or in an automobile headlight may simplify the requirements onany secondary optics and improve the illumination provided by the array.

However, if pcLEDs in an array are placed close together, optical crosstalk between adjacent pcLEDs may occur. That is, light emitted by apcLED may scatter into or otherwise couple into an adjacent pcLED andappear to originate from that other pcLED, preventing the desiredcompartmentalization of light.

The possibility of optical crosstalk between pixels in an arrayprohibits the use of a single shared phosphor layer on top an array ofLEDs. Instead, patterned phosphor deposition providing a discrete pixelof phosphor on each light emitting element is needed, in combinationwith reflecting sidewalls on the phosphor pixels.

If the spacing between the LEDs in the array is small, for instancesmaller than 10 or 20 microns, it is difficult to form reflecting sidewalls on the phosphor pixels with wet chemical or physical depositionmethods due to the high aspect ratios of the channels to be filled orcoated. The most common scattering layer used as a side coat for LEDscomprises TiO₂ scattering particles embedded in silicone. Another optionis a reflective metal layer, such as for instance aluminum or silver.Yet another option is a multilayer Distributed Bragg Reflector (DBR)structure formed from a stack of alternating layers of high and lowrefractive index material, which can provide very high reflectancedepending on design. To ensure uniform coating of such reflective layersor structures on the side walls of the phosphor pixels, the side wallsshould be accessible. If the aspect ratio of the gap between adjacentphosphor pixels is high, inhomogeneities in the reflective coatingthickness can be expected leading to non-uniform, non-optimal reflectingproperties.

This specification discloses methods that may be used to produce arraysof closely space phosphor pixels having thin side wall reflectors. Assummarized above, these methods employ patterned photoresist structuresin combination with vapor phase catalyzation of condensation curesilicone systems comprising phosphors.

The temperatures required to cure silicone or siloxanes are typicallyhigher than temperatures needed to ensure clean removal of photoresist,preventing general usage of photoresist patterned silicone. For example,if a photoresist is subjected to a typical silicone cure temperature of120 degrees Celsius, sufficient cross-linking occurs in the photoresistto prevent wash removal. Alternatively, if a maximum temperature of 90degrees Celsius is used to ensure later wash removal of the photoresist,the silicone is not adequately cured and partial removal or edge erosionof the silicone structures can occur during the wash step.

As seen in FIG. 5, a novel low temperature process 500 for patterning ofsilicone using conventional photoresists is described. Process 500allows for low temperature curing of silicone in conjunction withphotoresist patterning structures and includes a first step 510 ofapplying a photoresist to a substrate and patterning/removing thephotoresist to form desired structures. In a second step 520, cavitiesor regions defined after photoresist removal are at least partiallyfilled with a condensation cure silicone system. In a third step, acatalyst is added from the vapor phase 530. This is followed by asilicone condensation curing step 540. Then, either concurrently with asilicone condensation curing 540 or after curing, in a fifth step 550the photoresist is removed.

Positive photoresist compounds useful for this described low temperatureprocess can include photosensitive materials that are degraded by lightso that a developer will dissolve away deposited regions that areexposed to light. In effect, this leaves behind a coating where a maskwas placed (i.e. the film remains on the formerly dark portions of anilluminated resist). Positive resists typically need to be used at lowtemperatures, since they are susceptible to permanent crosslinking (alsocalled “hard bake”) at high temperatures, rendering the resist unable tobe removed afterwards by the stripping bath (typically a mild solventsystem).

The condensation cure silicone system can include curable polysiloxanecompositions that can provide acceptable cure rates without significantprocessing and storage difficulties

In certain embodiments, the condensation cure silicone system caninclude optional organic, inorganic, or organic/inorganic binder andfiller material. In one embodiment, light active phosphors, dyes, ornanoparticles can be bound together by the silicone. In otherembodiments, the silicone can form optical structures, including lenses,light guides, or refractive elements.

Catalysts for the condensation cure silicone system catalysts can beselected to minimize generation of species requiring removal, and/orshould not require high-temperature activation to enable curing atrelatively low temperatures and/or the use of heat-sensitive substrates.Compositions can employ catalysts that are relatively non-toxic, andthat are relatively stable in solution but relatively fast-curing upondrying. Catalysts can be effective in relatively low concentrations,and/or effective under relatively low (or no) moisture conditions.Catalysts that can be employed as a vapor phase can be used. In oneembodiment, vapor phase cure of the condensation cure silicone systemcan be conducted using basic or alkaline catalyzing agents. In anembodiment, superbase catalyzing agents such as described in U.S. Pat.No. 9,688,035 by Swier et. al. can be used. In some embodiments,silicone solid compositions manufactured using a superbase catalystexhibit enhanced cure rates, improved mechanical strength, and improvedthermal stability over similar compositions without the superbasecatalyst.

The term “superbase” used herein refers to compounds having a very highbasicity, such as lithium diisopropylamide. The term “superbase” alsoencompasses bases resulting from a mixing of two (or more) bases leadingto new basic species possessing inherent new properties. The term“superbase” does not necessarily mean a base that is thermodynamicallyand/or kinetically stronger than another. Instead, in some embodiments,it means that a basic reagent is created by combining thecharacteristics of several different bases. The term “superbase” alsoencompasses any species with a higher absolute proton affinity(APA=245.3 kcal/mole) and intrinsic gas phase basicity (GB=239kcal/mole) relative to 1,8-bis-(dimethylamino)-naphthalene.

Non-limiting examples of superbases include organic superbases,organometallic superbases, and inorganic superbases. Organic superbasesinclude but are not limited to nitrogen-containing compounds. In someembodiments, the nitrogen-containing compounds also have lownucleophilicity and relatively mild conditions of use. Non-limitingexamples of nitrogen-containing compounds include phosphazenes,amidines, guanidines, and multicyclic polyamines. Organic superbasesalso include compounds where a reactive metal has been exchanged for ahydrogen on a heteroatom, such as oxygen (unstabilized alkoxides) ornitrogen (metal amides such as lithium diisopropylamide). In someembodiments, the superbase catalyst is an amidine compound. In someembodiments, the term “superbase” refers to organic superbases having atleast two nitrogen atoms and a pKb of from about 0.5 to about 11, asmeasured in water.

In certain embodiments of the present invention, the superbase catalystis an organic superbase, such as any of the organic superbases asdescribed above or known in the art.

In a further embodiment, the superbase catalyst comprises:

1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU), (CAS #6674-22-2)

The amount of the superbase catalyst can vary and is not limiting.Typically, the amount added through vapor phase is a catalyticallyeffective amount, which may vary depending on the superbase selected,and vapor permeation properties of the siloxane polymer resin. Theamount of superbase catalyst is typically measured in parts per million(ppm) in the solid composition. In particular, the catalyst level iscalculated in regard to copolymer solids. The amount of superbasecatalyst added to the curable compositions may range from 0.1 to 1,000ppm, alternatively from 1 to 500 ppm, or alternatively from 10 to 100ppm, as based on the polymer resin content (by weight) present in thesolid compositions.

Silicone material or siloxanes can be selected for mechanical stability,low temperature cure properties (e.g. below 150-120 degrees Celsius),and ability to be catalyzed using vapor phase catalysts. In oneembodiment, organosiloxane block copolymers can be used.Organopolysiloxanes containing D and T units, where the D unit areprimarily bonded together to form linear blocks having 10 to 400 D unitsand the T units are primarily bonded to each other to form branchedpolymeric chains, which are referred to as “non-linear blocks” can beused.

Patterned vapor phase catalyzed silicone or siloxane materials such aspreviously described can be used in LED and microLED packaging. LEDpackages can contain phosphor material bound together using vapor phasecatalyzed silicone. In some embodiments, silicone bound phosphormaterial can form sidewalls that can be coated with metals, lightreflective materials, or mirrors (e.g. a distributed Braggreflector—“DBR mirror”).

The phosphors bound together using vapor phase catalyzed silicone can bepositioned on a substrate formed of sapphire or silicon carbide that isable to support an epitaxially grown or deposited semiconductor n-layer.A semiconductor p-layer can be sequentially grown or deposited on then-layer, forming an active region at the junction between layers.Semiconductor materials capable of forming high-brightness lightemitting devices can include, but are not limited to, Group III-Vsemiconductors, particularly binary, ternary, and quaternary alloys ofgallium, aluminum, indium, and nitrogen, also referred to as III-nitridematerials.

Phosphors can include one or more wavelength converting materials ableto create white light or monochromatic light of other colors. All oronly a portion of the light emitted by the LED may be converted by thewavelength converting material of the phosphor. Unconverted light may bepart of the final spectrum of light, though it need not be. Examples ofcommon devices include a blue-emitting LED segment combined with ayellow-emitting phosphor, a blue-emitting LED segment combined withgreen- and red-emitting phosphors, a UV-emitting LED segment combinedwith blue- and yellow-emitting phosphors, and a UV-emitting LED segmentcombined with blue-, green-, and red-emitting phosphors. Phosphors boundtogether with silicone can be molded, dispensed, screen printed,sprayed, or laminated.

In one embodiment, the light reflection material can be a metallizedlayer. In other embodiments, a dielectric mirror or DBR can be used. Insome embodiments, light reflection material can include a thin layer ofa binder such as silicone and light reflective particles. Lightreflective material can also include organic, inorganic, ororganic/inorganic binder and filler material. For example,organic/inorganic binder and filler can be, for example, silicone withembedded reflective titanium oxide (TiO₂), SiO₂, or otherreflective/scattering particles. Inorganic binders can include sol-gel(e.g., a sol-gel of TEOS or MTMS) or liquid glass (e.g., sodium silicateor potassium silicate), also known as water glass. In some embodiments,binders can include fillers that adjust physical properties. Fillers caninclude inorganic nanoparticles, silica, glass particles or fibers, orother materials able to improve optical or thermal performance. Thelight reflective material can be applied to the sidewalls by variousprocesses, including evaporative deposition (for metals) atomic layerdeposition (for DBR mirrors), or molding, dispensing, screen printing,spray, or lamination (for reflective particles in a binder).

In still other embodiments primary or secondary optics can be attachedor positioned near the silicone bound phosphors in LED package. Opticscan include concave or convex lenses, lenslet arrays, graded index lens,reflectors, scattering elements, beam homogenizers, diffusers, or otherlight focusing or blurring optics. Protective layers, transparentlayers, thermal layers, or other packaging structures can be used asneeded for specific applications.

As seen in FIGS. 6A-6G, a process is described for forming a patternedphosphor structure using positive photoresist and vapor phase catalyzedsilicone containing particulate phosphors. As seen in FIG. 6A, astructure 600A includes a substrate 610 supporting a removable positivephotoresist 620 and a silicone structure 630 containing optionalphosphors, dyes, light activated nanoparticles, fillers, or othermaterials.

FIG. 6B illustrates structure 600B defined after removal of the positivephotoresist, leaving freestanding silicone 630 pillars or forms, withcavities 622 defined adjacent to the silicone structures 630. Thecavities can include but are not limited to holes, channels, regularpatterns such a rectangular layouts, checkerboard layouts, curved orserpentine layouts, or hexagonal layouts.

FIG. 6C illustrates a structure 600C after application of a reflectivelayer 640 over the silicone structure top, sidewalls, and substrate 610.The reflective layer can be a metal, a dielectric mirror, or reflectiveparticles contained in a binder.

FIG. 6D illustrates a structure 620D after infill of cavities 622 withsilicone and optional phosphors, dyes, light activated nanoparticles,fillers, or other materials. The silicone can be identical to that usedin FIGS. 6A-6C, or other types of silicone systems and phosphors can beused. For example, a high temperature silicone system that does notrequire vapor catalyzation can be used with a set of phosphors havingdifferent emission properties.

FIG. 6E illustrates a structure 600E after removal of the top reflectivelayer by grinding, polishing, or etching.

FIG. 6F illustrates a structure 600F after flipping and attachment to anLED substrate that includes active light emitters. The LED substrate canbe a microLED with micron scale features and/or millimeter scale pixels.

FIG. 6G illustrates a structure 600G after removal of the substrate 610and top reflective layer by conventional release techniques and/orgrinding, polishing, or etching. This leaves vertical reflectivecoatings 640 on the sidewalls between silicone structures 630, providingoptical isolation between phosphor pixel structures.

FIG. 7 illustrates an intermediate structure 700 corresponding to theprocessing step illustrated by FIG. 6C. The includes a checkerboardpattern with one half of the phosphor array being formed and cured, andreflective layer formed to cover vapor catalyzed silicone containingparticulate phosphor “islands” 730. The cavities channels or grooves(gaps) 722 between the islands 730 will be infilled with additionalphosphor in a next step, cured, and any applied reflective material on atop and bottom surface removed prior to attachment of both the phosphorstructure to an LED array and any additional optics.

Light emitting arrays or microLED arrays such as disclosed herein maysupport a wide range of applications that benefit from fine-grainedintensity, spatial, and temporal control of light distribution. This mayinclude, but is not limited to, precise spatial patterning of emittedlight from blocks or individual LEDs. Depending on the application,emitted light may be spectrally distinct, adaptive over time, and/orenvironmentally responsive. In some embodiments, the light emittingarrays may provide pre-programmed light distribution in variousintensity, spatial, or temporal patterns. The emitted light may be basedat least in part on received sensor data and may be used for opticalwireless communications. As noted above, associated optics may bedistinct at single or multiple LED level. An example light emittingarray may include a device having a commonly controlled central block ofhigh intensity LEDS with an associated common optic, whereas edgepositioned LEDs may have individual optics. Common applicationssupported by light emitting LED arrays include video lighting,automotive headlights, architectural and area illumination, streetlighting, and informational displays.

Programmable light emitting arrays may be used to selectively andadaptively illuminate buildings or areas for improved visual display orto reduce lighting costs. In addition, light emitting arrays may be usedto project media facades for decorative motion or video effects. Inconjunction with tracking sensors and/or cameras, selective illuminationof areas around pedestrians may be possible. Spectrally distinct LEDsmay be used to adjust the color temperature of lighting, as well assupport wavelength specific horticultural illumination.

Street lighting is an important application that may greatly benefitfrom use of programmable light emitting arrays. A single type of lightemitting array may be used to mimic various street light types,allowing, for example, switching between a Type I linear street lightand a Type IV semicircular street light by appropriate activation ordeactivation of selected LEDs. In addition, street lighting costs may belowered by adjusting light beam intensity or distribution according toenvironmental conditions or time of use. For example, light intensityand area of distribution may be reduced when pedestrians are notpresent. If LEDs of the light emitting array are spectrally distinct,the color temperature of the light may be adjusted according torespective daylight, twilight, or night conditions.

Programmable light emitting LEDs are also well suited for supportingapplications requiring direct or projected displays. For example,automotive headlights requiring calibration, or warning, emergency, orinformational signs may all be displayed or projected using lightemitting arrays. This allows, for example, modifying directionality oflight output from a automotive headlight. If a light emitting array iscomposed of a large number of LEDs or includes a suitable dynamic lightmask, textual or numerical information may be presented with user guidedplacement. Directional arrows or similar indicators may also beprovided.

Many modifications and other embodiments of the invention will come tothe mind of one skilled in the art having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is understood that the invention is not to be limited tothe specific embodiments disclosed, and that modifications andembodiments are intended to be included within the scope of the appendedclaims. It is also understood that other embodiments of this inventionmay be practiced in the absence of an element/step not specificallydisclosed herein.

1. An array of phosphor pixels comprising: a plurality of phosphor pixels spaced apart from each other, each phosphor pixel comprising side walls facing adjacent pixels in the array, and a top surface and a bottom surface having the side walls in between them; and a plurality of reflective structures disposed between the side walls of adjacent phosphor pixels, and disposed at alternating top surfaces and bottom surfaces of adjacent phosphor pixels.
 2. The array of phosphor pixels in claim 1, wherein each phosphor pixel comprises phosphors in a silicone or siloxane.
 3. The array of phosphor pixels in claim 1, wherein the reflective structures each comprise a distributed Bragg reflector.
 4. The array of phosphor pixels in claim 1, wherein the reflective structures each comprise a binder and light reflective particles.
 5. The array of phosphor pixels in claim 4, wherein the binder is an inorganic binder.
 6. The array of phosphor pixels in claim 4, wherein the binder is an organic binder.
 7. The array of phosphor pixels in claim 1, wherein the plurality of reflective structures are disposed as walls between the side walls of adjacent phosphor pixels and disposed as planar surfaces at the alternating top surfaces and bottom surfaces of adjacent pixels, the planar surfaces being perpendicular to the walls, and adjacent planar surfaces disposed at respective top and bottom surfaces are connected to each other through walls between them.
 8. The array of phosphor pixels in claim 1, wherein adjacent phosphor pixels have top surfaces that are not flush those of their neighbors and bottom surfaces that are not flush with those of their neighbors.
 9. An array of phosphor pixels comprising: a plurality of phosphor pixels spaced apart from each other, each phosphor pixel comprising side walls facing adjacent pixels in the array, and a top surface and a bottom surface having the side walls in between them; and a plurality of reflective structures disposed between the side walls of adjacent phosphor pixels, and disposed at alternating bottom surfaces of adjacent phosphor pixels to form a checkerboard pattern.
 10. The array of phosphor pixels in claim 1, wherein the reflective structures are not disposed on the top surfaces of any of the phosphor pixels.
 11. The array of phosphor pixels in claim 9, wherein each phosphor pixel comprises phosphors in a silicone or siloxane.
 12. The array of phosphor pixels in claim 9, wherein the reflective structures each comprise a distributed Bragg reflector.
 13. The array of phosphor pixels in claim 9, wherein the reflective structures each comprise a binder and light reflective particles.
 14. The array of phosphor pixels in claim 13, wherein the binder is an inorganic binder.
 15. The array of phosphor pixels in claim 13, wherein the binder is an organic binder.
 16. The array of phosphor pixels in claim 9, wherein the reflective structures are disposed as reflective walls between the side walls of adjacent phosphor pixels and disposed as planar surfaces at bottom surfaces of alternating adjacent phosphor pixels, so that the reflective walls disposed on the side walls of one of the adjacent phosphor pixels are connected through each other by the planar surface, and the reflective walls disposed on the other of the adjacent phosphor pixels are not connected through each other by the planar surface.
 17. The array of phosphor pixels in claim 9, wherein the reflective structures are disposed as reflective walls between the side walls of adjacent phosphor pixels and disposed as planar surfaces at bottom surfaces of alternating adjacent phosphor pixels, the planar surfaces being disposed on and in direct contact with a substrate, the substrate directly contacting bottom surfaces of alternate phosphor pixels.
 18. The array of phosphor pixels of claim 17, wherein the top surfaces of the phosphor pixels are in direct contact with a light emitting device.
 19. An array of phosphor pixels comprising: a plurality of phosphor pixels spaced apart from each other, each phosphor pixel comprising side walls facing adjacent pixels in the array; and a plurality of reflective structures disposed between the side walls of adjacent phosphor pixels; the spacing between adjacent phosphor pixels being equal to the thickness of the reflective structure disposed between them, which is less than or equal to about 3 microns.
 20. The array of phosphor pixels of claim 19, wherein the reflective structures comprise Distributed Bragg Reflector structures. 